The present invention relates to controlling dust and other contaminants on paper machinery or similar apparatus.
A necessary step in presently known paper making, tissue making and similar machinery is the drying of the moist paper web on a drum, known as a xe2x80x9cYankee dryer.xe2x80x9d The heated Yankee dryer rotates constantly, with wet paper web being taken up at one spot on the rotation, and being dried before being scraped off the dryer at another spot in the rotation. After being scraped off the dryer, the web usually passes through a sensor, measuring the moisture and thickness of the web, and then is taken up by a reel drum.
The paper web is scraped off the Yankee dryer by a blade known as a xe2x80x9ccreping doctor.xe2x80x9d Usually following the creping doctor is a xe2x80x9ccleaning doctor,xe2x80x9d which removes any stray material that was left after the paper web is scraped off the dryer. Finally, the dryer is sprayed with a coating prior to taking up a new section of paper web.
The creping and cleaning operations create dust, in the form of fibers, tendrils, tiny scraps of paper, etc. Other locations in the machinery also create dust as a byproduct of the operation. The greatest quantity of dust is usually generated below the paper web sheet because of the action of the creping doctor and the cleaning doctor. Controlling the dust is important. Dust can detrimentally affect workers"" health, create a fire hazard, ruin the machinery, and interfere with the sensor ""s operation.
The dust is not the only undesirable byproduct of the operation. Excess moisture, released from the drying, the cleaning and coating solutions or other sources can also adversely affect the operation.
The prior art has attempted to control dust by a variety of methods. The majority of these methods involve attempting to collect dust at or very near the creping doctor. See, e.g., U.S. Pat. No. 4,019,953. However, almost invariably, the means used are ineffective because the prior art devices make no allowance for the moisture generated by the paper making procedure. This moisture will clog the dust control devices used by the prior art and so interfere with the dust take-up. A clogged device cannot remove dust from the machinery. This is especially true for the prior art devices which attempt to control the dust at the creping doctor blade. These devices are impractical and quickly fail because of the moisture in the creping doctor blade area which quickly clogs an exhaust hood or other dust control method. Thus, the prior art has failed to solve the problem of moisture-associated clogging in paper making and similar machinery.
Moreover, a substantial amount of dust and other contaminants is carried by one or more xe2x80x9cboundary layersxe2x80x9d along the web, after the web has been creped off the Yankee dryer. A boundary layer is usually from four to six inches thick, and located along the top and bottom of the web, with the bottom boundary layer usually carrying the majority of the dust and contaminants. Heretofore, boundary layer dust has not been adequately captured or eliminated from the system. Nor has the prior art adequately controlled dust that originally was carried by a boundary layer and subsequently sloughs off the boundary layer as the web travels towards the reel drum.
Accordingly, it is an object of the present invention to control both dust and moisture in paper machinery and the like.
It is a further object of the present invention to control both dust and moisture simply and efficiently.
It is a further object of the present invention to control both dust and moisture through apparatus and methods that can be added to already existing machinery.
It is a further object of the present invention to control boundary layer dust and moisture.
The present invention comprises methods and apparatus for controlling dust. In the preferred embodiments, a foil, an air ramp, a baffle, and exhaust hood are provided to the underside of the web after it is creped off the Yankee dryer. The foil separates the boundary layer air containing dust and moisture and, at the same time, provides web stability. The foil directs the air to an air ramp, which in turn directs the air along the baffle into an exhaust hood. A cleaning jet prevents the dust from sticking to the interior surface of the exhaust hood and an external exhaust system may then remove the moist dust from the exhaust hood.
In especially preferred embodiments, the foil is comprised of porous metal, and is internally pressurized. That pressurization provides air flow through the porous metal and creates an xe2x80x9cair lubricantxe2x80x9d for the web.